Investigation and Characterization of Lignin Precipitation in the LignoBoost Process

Abstract

Lignin of high purity can be separated from black liquor using the LignoBoost process, of which the overall efficiency is largely dependent on the precipitation yield of lignin, which depends on the properties of black liquor and process conditions. In this paper, the influences of process conditions on the precipitation yield of lignin from mixed hardwood/softwood black liquor were investigated. The Klason and standard UV method were used to determine lignin concentration. The chemical and structural properties of lignin were also analyzed. The results showed that the precipitation yield of lignin increased along with a decrease in pH and temperature, or with an increase in the ion strength of black liquor, and the yield was lower when mixed softwood/hardwood black liquor was used. It also showed that at a higher precipitation yield the precipitated lignin had a lower average molecular weight but had higher methoxyl and phenolic hydroxyl content.

Keywords:

• Kraft lignin
• precipitation
• black liquor
• pH
• ion strength
• molecular weight
• ¹H NMR spectra
• carbohydrates analysis

Acknowledgments

The authors are grateful to Lena Fogelquist and Tommy Friberg for their help with the experimental work. The 200 MHZ ¹³C NMR spectroscopy was performed by Göran Karlsson and Maxim Mayzel at the Swedish NMR centre, Gothenburg. This work was conducted within the Chalmers Energy Initiative.